Project Summary Nearly six million adults currently suffer from heart failure in the United States. Although current therapies have improved outcomes, heart failure continues to be associated with low quality of life, increased risk for hospitalization and reduced survival. Thus, novel treatment strategies are required for further improvements to occur. The development of heart failure is accompanied by progressive changes in cardiac structure that impede normal function, a process termed cardiac remodeling. Deposition of fibrous tissue is an important component of this process. Fibrosis leads to cardiac stiffness, disordered electrical conduction and impaired coronary perfusion, which ultimately result in diastolic and/or systolic dysfunction, arrhythmias and ischemic stress. Although inhibiting cardiac fibrosis has been an important goal, there are no recognized strategies for achieving this goal, and progress has been impeded by a peripheral knowledge about how the complex process of collagen secretion/deposition is regulated. Better understanding of the mechanisms responsible for the inappropriate deposition of collagen is needed to devise effective therapeutic strategies. A large portion of newly translated procollagen is degraded prior to exiting the cell. Previous reports and our preliminary data indicate that alteration of this intracellular turnover strongly influences procollagen secretion and suggest that the endoplasmic reticulum (ER)-resident enzyme, UGGT1, plays a key role in modulating this process. Although this under-appreciated control of collagen deposition represents a potential therapeutic target(s) for treating fibrosis, there is insufficient information about it. The present proposal will study this novel mechanistic control using both in vitro mouse and human cultured cells and in vivo mouse models by addressing the following three specific aims. Aim 1) To determine the contribution of ER ?folding time? to procollagen secretion in cultured mouse and human cardiac myofibroblasts. 2) To quantify misfolded procollagen turnover and determine the mechanisms involved in mouse and human cultured cardiac myofibroblasts. And 3) To determine the effect of modulation of ER turnover in an animal model of cardiac fibrosis. Aim 1 will use genetic manipulation of critical mediators of the UGGT1 folding cycle to assess their effects on both procollagen secretion and global protein secretion in mouse and human cardiac myofibroblasts. Aim 2 will use pharmacologic inhibitors and genetic manipulation to study the degradative mechanisms responsible for removing the procollagen that is not secreted (with particular focus on autophagy of procollagen ?1(I)). Aim 3 will use conditional deletion or overexpression of UGGT1 to address its effect on cardiac structure/function in a mouse model of reactive cardiac fibrosis (i.e., Angiotensin II infusion). The proposed work should provide new insights into cardiac fibrosis mechanisms that will help our long-term goal of identifying novel therapeutic targets to inhibit fibrosis and improve clinical outcomes in heart failure patients.